We have isolated a substance from rabbit plasma which stimulates prostaglandin synthetase, maintains coronary vascular tone, and augments autoregulation in isolated rabbit hearts. This active material migrates as a single substance on thin-layer chromatograms. We propose to: (1) confirm its purity using methods such as gasliquid or column chromatography; (2) identify this material chemically through the use of mass or infrared spectroscopy, nuclear magnetic resonance, elemental analysis or other methods; and (3) isolate and identify this vasoactive substance from the blood of animals other than rabbits. BIBLIOGRAPHIC REFERENCES: Moretti, R.L., S. Abraham and R.R. Ecker, The simulation of cardiac prostaglandin production by blood plasma and its relationship to the regulation of coronary flow in isolated isovolumic rabbit hearts, Circ. Res. 39:231-238, 1976. Philpott, D.E., R.L. Moretti, G. Harrison, G. Klein, S. Abraham and R. Kato, Effects of extended retrograde perfusion on excised hearts, (abstract) Presented at the 8th Western Regional Meeting of Electron Microscopists, San Fransicso, California, February 10-12, 1977.